This invention relates to motor vehicle instrument panels having an integral air bag deployment door defined by a tear seam and more particularly to a tether for a potentially frangible air bag door when it is separated at very low temperatures from the instrument panel and then because of cold embrittlement from a flexible hinge that is integral with the door and normally provides through bending movement for opening swinging movement of the door and its retention to the vehicle structure at higher temperatures.
Presently, most passenger side air bag doors are formed in an air bag cover that is separate from the instrument panel because the latter is made of various commercially available thermoplastic materials that are particularly well suited to meeting the requirements of its application but are not well suited to meeting the requirements of an air bag door that is defined by a tear seam formed in a single layer instrument panel. For example, the plastics materials used to make such an instrument panel must have a certain degree of stiffness and high heat resistance to meet the requirements of its application but the materials that are currently available for such an application do not retain ductility and become embrittled at very low or cold temperatures. This lack of low temperature ductility is undesirable for air bag deployment where the air bag door is formed integral with and defined by a tear seam that is formed in the instrument panel and is torn to provide an air bag deployment opening in the panel by the force of the inflating air bag acting on the panel in the area of the tear seam. Styrene-maleic anhydride, polypropylene, polycarbonate, polyphenylene oxide and polyurethane are examples of thermoplastic materials that are suitable for such an instrument panel but have not exhibited the required ductility for such a tear-open air bag door at very low temperatures and as a result a portion or portions of the door may fracture and separate from the instrument panel on deployment of the air bag and undesirably enter the space of the passenger compartment. To meet extreme low temperature requirements, many various designs of an air bag deployment door have been proposed wherein the door is made separate from the panel and is installed as a hinged door assembly on the instrument panel so that the door is not prone to fracture from cold embrittlement by the force of the inflating air bag as it freely swings open on its hinge from the force of the air bag.
Costs can be reduced, quality can be improved and styling can be enhanced by molding the instrument panel and the air bag cover including an integral air bag deployment door in one piece at the same time out of the same commercially available material. That is provided that the normal material requirements for the instrument panel are not sacrificed while the safe assured operability of the integral air bag deployment door is still somehow retained at reasonable cost even though its plastics material is not well suited thereto.
In the present invention, a molded motor vehicle instrument panel made of a thermoplastic material well suited for the primary purpose of such a panel has an integral air bag deployment door for a passenger side air bag that is safely retained to the vehicle structure in a very cost effective manner. The air bag door is defined by a tear seam in the panel and is normally retained by an integral flexible mounting/hinge flange to a part of the vehicle structure when the seam is torn by the inflating air bag and wherein this flange which before was integral with both the door and the panel is then separated from the main body of the panel while remaining integral with the door and bends to allow the door to swing open to allow deployment of the air bag through an opening in the instrument panel while retaining same to the vehicle structure as the door is then free of the instrument panel. At very low temperatures, a portion of the air bag door can break away from the mounting/hinge flange where it joins therewith because of plastic embrittlement at these low temperatures and the high bending stresses encountered at this juncture.
This separation of the broken door portion from the vehicle structure is prevented by bonding a layer of second plastics material over the juncture zone and an adjoining inside surface of the potentially frangible door portion and an adjoining one side of the mounting/hinge flange. The second plastics material has the physical characteristic of remaining ductile to a substantial degree at low temperatures substantially below the temperature at which the first plastics material becomes brittle. The bonded layer thus forms a tether that tethers the frangible door portion to the mounting/hinge flange in a flexible manner when this door portion breaks away from the flange because of embrittlement of the first plastics material at the low temperatures on tearing of the tear seam and opening movement of the door by the inflating air bag pressing against the inside surface of the frangible door portion. This allows the broken door portion to continue movement in it opening direction to allow continued deployment of the air bag while the broken door portion remains connected by the flexible tether to the mounting/hinge flange and thereby the vehicle structure.
The instrument panel and the air bag deployment door tethering layer may be formed in various ways including injection molding the panel and injection molding, spraying or low pressure molding the tethering layer in a second step. Such formation of the tether in place as a bonded layer is particularly advantageous from both a cost and production standpoint as it becomes integral with the instrument panel and there is no need to inventory a separate tether that must then be fastened by some form of fastening means to both the mounting/hinge flange and the door. Furthermore, the bonding of the tethering layer to the inside surface of the door hides its presence from view which is desirable from an appearance or styling standpoint.
It is therefore an object of the present invention to provide a new and improved method of forming a motor vehicle instrument panel with an integral air bag deployment door and a flexible tether for the door.
Another object is to provide a new and improved method of forming a motor vehicle instrument panel with an integral air bag deployment door and a flexible tether for the door at low cost and of high quality and to meet certain styling desires.
Another object is to provide a method of forming a motor vehicle instrument panel with a tethered air bag deployment door wherein the panel including the door is formed of a plastics material suited to meet the requirements of an instrument panel and the tether is formed of a layer of plastics material that spans a potential fracture zone in the door and remains ductile at low temperatures that cause embrittlement of the door that could result in the fracturing of a portion of the door at thus fracture zone on air bag deployment and loss of its retention to the vehicle structure but for the tethering layer.
Another object is to provide a method of forming a motor vehicle instrument panel including an air bag deployment door that is defined by a tear seam molded in the panel wherein the panel is formed of a plastics material suited to its requirements and the door is retained to the vehicle structure on breaking away at very cold temperatures by a flexible layer of plastics material that is formed in place over an inside surface of the door and one side of a mounting/hinge flange that is molded integral with the inside surface of the door and normally retains the air bag door to the vehicle structure on opening movement.
Another object is to provide a low cost, high quality motor vehicle instrument panel with flexibly tethered air bag deployment door produced by the above method.
A second aspect of the present invention includes an automotive air bag cover assembly comprising a hinge panel that is connected, in a layered disposition, to an inside surface of at least one of the integral air bag cover and instrument panel. The instrument panel comprises a first plastics material and is configured to mount in the passenger compartment of the motor vehicle. The air bag door panel also comprises the first plastics material and is formed with the instrument panel as a single integral panel. The door panel is at least partially surrounded by the instrument panel. One object of this second aspect of the present invention is to simplify and accelerate the manufacture of hinged integral panels by providing a hinge panel that is insert molded into an inside surface of at least one of the instrument panel and the door panel.
Another object of the second aspect of the present invention is to provide a hinge panel to act as a primary hinge between the door panel and the instrument panel during air bag deployment. The hinge panel spans a panel juncture zone between the door panel and the instrument panel.
Another object of the second aspect of the present invention is to aid in bending the first plastics material at the hinge location by providing a panel juncture zone that includes a styling groove separating at least a portion of the door panel and the instrument panel. The styling groove may also function as a tear seam.
Another object of the second aspect of the present invention is to guide tearing around the door panel when the air bag inflates by providing a panel juncture zone that includes a weakened tear seam separating at least a portion of the door panel and the instrument panel.
Another object of the second aspect of the present invention is to provide a hinge that includes a hinge panel edge aligned with at least a portion of the tear seam to act in guiding tearing along the tear seam as the door is forced open during air bag inflation.
Another object of the second aspect of the present invention is to prevent hinge panel fracture at low temperatures by providing a hinge panel comprising a second plastics material that is more ductile and less brittle at low temperatures than the first plastics material.
Another object of the second aspect of the present invention is to prevent hinge panel fracture by providing a hinge panel comprising metal.
Another object of the second aspect of the present invention is to provide a means of securing the door panel to a structural member during deployment by providing a hinge flange that extends transversely inward from the inside surface of the door panel. The hinge flange is configured to secure the door panel to a structural member. The hinge panel spans a juncture zone between the hinge flange and door panel in a layered disposition with a portion of the hinge panel being attached to the hinge flange.
Another object of the second aspect of the present invention is to provide a means for supporting an air bag canister assembly on the instrument panel by providing a collar that extends transversely inward from the inside surface of the instrument panel and from around the door panel. The collar defines a door-collar interface along the region where the collar extends from the panel. The hinge panel spans the door-collar interface, one portion of the hinge panel being attached to the collar and another portion of the hinge panel being attached to the door panel.
Another object of the second aspect of the present invention is to provide a method for making an air bag cover assembly. The method includes providing a mold having first and second mold portions. The first and second mold portions form a mold cavity when closed together. The mold cavity has a shape that complements the shape of the integral instrument and door panel and the hinge panel. After being formed separately, the hinge panel is placed in the second mold portion. The mold is then closed and the first plastics material is introduced into the mold cavity in molten form. The molten first plastics material is then allowed to conform to the shape of the mold cavity and to solidify in the mold cavity. The mold is then opened and the completed assembly is removed from the mold.
The method may also include formation of the hinge panel from the second plastics material and the selection of a second plastic material that is more ductile and less brittle at low temperatures than the first plastics material.
The method may alternatively include the provision of a hinge panel comprising metal. In applications where an edge of the hinge panel is aligned with a tear seam to guide tearing along the tear seam, metal is generally preferred over plastic due to increased rigidity which aids in evenly distributing door opening forces along a tear seam to promote more uniform tear seam fracture and subsequent door opening.
The method may also include the placement of the hinge panel on the mold cavity surface of the second mold portion in a position spanning a portion of the mold configured to form the panel juncture zone between the instrument panel and door panel portions of the integral panel. The mold cavity surface of the second mold portion may be shaped to form a hinge-flange that protrudes transversely inward from the door panel portion of the integral panel. In this case, the hinge panel is placed on the mold cavity surface of the second mold portion in a position spanning a portion of the mold configured to form a flange juncture zone between the hinge-flange and the door panel.
These and other objects, advantages and features of the present invention will become more apparent from the following description and the accompanying drawings wherein: